The invention relates to the production of yellow bis(3-[triethoxysilyl]propyl)polysulfane.
Bis(3-[triethoxysilyl]propyl)disulfane can be produced by the reaction of chloropropyltriethoxysilane with sodium sulfide (Na2S) and sulfur. The chloropropyltriethoxysilane used can be produced by ethanolysis of chloropropyltrichlorosilane. As is known from DE 20 61 189 and DE 32 36 628, a completely reacted product with only a very small proportion of chloropropylmonochlorodiethoxysilane is obtained therefrom. This completely reacted chloropropyltriethoxysilane is referred to below as xe2x80x9cneutralxe2x80x9d.
If the neutral chloropropyltriethoxysilane is reacted with sodium sulfide (Na2S) and sulfur to form bis(3-[triethoxysilyl]propyl)disulfane, a dark-yellow to red coloured product (iodine colour value xe2x89xa720 mg iodine/100 ml) is obtained. However, a light-yellow product, which cannot be obtained from neutral chloropropyltriethoxysilane, has been introduced on to the market. In order to obtain light-yellow bis(3-[triethoxysilyl]propyl)disulfane (iodine colour value xe2x89xa610 mg iodine/100 ml), a so-called residual acid content must be present in the chlororopyltriethoxysilane in the form of chloropropylmonochlorodiethoxysilane. This can be achieved in that the ethanolysis reaction is not fully completed. However, in operating practice, this measure results in not inconsiderable additional outlay, particularly since the residual acid content has to be kept within a very narrow range and therefore the reaction has to be terminated very specifically at a certain point shortly before complete conversion.
Acidification of the neutral chloropropyltriethoxysilane with alcoholic hydrochloric acid before the reaction with the above-mentioned thionating agents also leads not to light-yellow coloured bis(3-[triethoxysilyl]propyl) disulfane but again to a dark-yellow to red coloured compound.
From EP 0963 995 a process is known for the production of short-chain polysulfide silanes from M2S or NS with M=alkali metal, ammonium and N =alkaline earth metal, zinc, sulfur and halopropyltrialkoxysilane.
Furthermore, from DE 100 34 493.3 a process is known for the production of organosilyl alkyl polysulfanes by reduction of the sulfur chain length with M2S and organosilyl alkyl halide. The organosilyl alkyl polysulfane with the original long sulfur chain can also be reacted with the M2S and the organosilyl alkyl halide as soon as it is formed from organosilyl alkyl halide and M2Sy.
The disadvantage of these known processes lies in the fact that a product with a dark-yellow to red colour is obtained.
From DE 10024037.2 a process for the production of light-yellow bis(3-[triethoxysilyl]propyl)tetrasulfane is known, wherein chloropropyltrichlorosilane is added to neutral chloropropyltriethoxysilane and then reacted with sodium polysulfide or Na2S and sulfur in ethanol.
The object of the invention is to provide an alternative process with the aid of which a yellow bis(3-[triethoxysilyl]propyl)polysulfane is obtained.
The invention provides a process for the production of yellow bis(3-[triethoxysilyl]propyl)polysulfane with an average sulfur chain length of less than 4, preferably less than 3.1, particularly preferably less than 2.5, and an iodine colour value of xe2x89xa610 mg iodine/100 ml, preferably 5-7 mg iodine/100 ml, which is characterised in that neutral chloropropyltriethoxysilane is mixed with chloropropyltrichlorosilane and then reacted with sodium sulfide (Na2S) and sulfur, disodium tetrasulfide (Na2S4) and Na2S or disodium trisulfide (Na2S3) and Na2S in ethanol. The disodium trisulfide (Na2S3) can be a 1:1 mixture of Na2S2 and Na2S4.
The bis(3-[triethoxysilyl]propyl)polysulfane can be a polysulfane mixture.
In a preferred embodiment, the bis(3-[triethoxysilyl]propylsulfane can be a bis(3-[triethoxysilyl]propyl)disulfane or bis(3-[triethoxysilyl]propyl) trisulfane.
This process has the advantage that the ethanolysis reaction does not have to be specifically terminated at a certain point shortly before complete conversion, but can be carried out to complete conversion to neutral chloropropyltriethoxysilane. The small quantity of chloropropylmonochlorodiethoxysilane required for the production of light-yellow bis(3-[triethoxysilyl]propyl)polysulfane can be achieved simply by adding chloropropyltrichlorosilane to neutral chloropropyltriethoxysilane.
Chloropropyltrichlorosilane can be added to a solution of neutral chloropropyltriethoxysilane and ethanol or chloropropyltrichlorosilane can be added to neutral chloropropyltriethoxysilane and ethanol then added.
Chloropropyltrichlorosilane can be added in quantities of 0.1-20 wt. %, preferably 0.5-5 wt. %, particularly preferably 0.8-1.2 wt. %. The ratio of chloropropyltriethoxysilane: Na2S: S or sodium polysulfide determines the sulfur chain length in bis(3-[triethoxysilyl]propyl)polysulfane.
The reaction mixture can be heated before adding sodium polysulfide and Na2S or Na2S and sulfur, preferably to temperatures of 20-90xc2x0 C.
Bis (3- [triethoxysilyl]propyl) polysulfane produced by the process according to the invention has an iodine colour value of xe2x89xa610 mg iodine/100 ml.